U.S. Pat. No. 6,280,419 describes a needle guard device that automatically engages with a needle when the tip of the needle is withdrawn into an enclosing volume or cavity contained within the protective device. The mechanism within the needle guard for engaging with the needle operates on the principle of a canting plate that has a hole through which the shaft of the needle passes. Before deployment of the guard, the plate carrying the hole is oriented perpendicularly to the axis of the needle shaft, and a tight sliding fit exists between the needle shaft and the perimeter of the hole. Once the tip of the needle has been withdrawn into the guard, the plate is caused by a spring to “cant” or rotate from its perpendicular orientation with respect to the needle shaft. By reason of the tight sliding fit between the shaft and the hole in the canting plate, the edge of the perimeter of the hole forcefully engages with the surface of the needle, preventing further retraction of the needle in the direction that would cause the canting plate to cant at an even further angle.
In the design of the needle guard of U.S. Pat. No. 6,280,419, the canting plate acts to arrest the needle shaft against further withdrawal of the needle shaft through the needle guard's cavity. The canting action described above occurs when the needle tip has been withdrawn into the cavity and a sensing arm connected to the canting plate is able to shift its position due to the retraction of the needle tip past an opening in a limb of the sensing arm through which the needle passes prior to the initiation of locking action.
In the specific design of the referenced patent, provision is made for a wire to be present, passing through the core of the needle and the body of the needle guard. As the needle guard and needle are retracted, they slide along this wire. To permit such movement to continue after the needle tip has entered within the cavity of the needle guard, the opening in the limb on the sensing arm is in the form of a slot. The bottom of the slot is large enough to permit passage of the needle shaft before the needle guard is deployed. The slot above the bottom is of a reduced width, sufficient to allow passage of the wire, but narrow enough to prevent the reemergence of the needle tip from the needle guard, once the needle tip has withdrawn from the hole in the limb of the sensing arm. The reemergence of the needle is prevented in this design by the presence of the sides of the limb on the sensing arm that define the borders of the slot. These sides remain in the path that the needle tip would have to follow if it were to attempt to re-emerge from the needle guard.
This system for preventing reemergence of the needle tip from the needle guard depends critically upon the engagement of the sidewall of the needle with the sides of the slot in the locking limb on the sensing plate. As the needle wall is of a relatively small thickness, this method for preventing reemergence of the needle tip does not provide maximum reliability.
The present invention provides a system for preventing reemergence of the needle tip which is an alternative to, and may be more reliable than, the system described above.
The invention in its general form will first be described, and then its implementation in terms of specific embodiments will be detailed with reference to the drawings following hereafter. These embodiments are intended to demonstrate the principle of the invention, and the manner of its implementation. The invention in its broadest and more specific forms will then be further described, and defined, in each of the individual claims which conclude this Specification.